This invention relates generally to a blower motor control circuit and in particular to a device for protecting the circuit from overloads at the lower speeds of a blower motor.
It has been a practice in the past to control the speed of a motor vehicle air conditioning and heater blower motor through the use of one and more voltage-dropping resistors. Such resistors may be used singularly or in combination to provide varying speeds for a single speed series connected wire-wound or permanent magnet motor. So far as known, it has also been a practice to position such resistors in the air stream of a blower motor to dissipate the heat generated by flow of current through the resistors at the lower motor speeds. It has also been a practice to provide a main fuse for the blower motor control circuit which fuse has sufficient amperage to handle the current going through the blower motor at its high speed.
Malfunctions may occur in the blower system which can cause fire hazards. Such malfunctions may typically be a loss of lubricant in the blower motor bearing causing the motor to lock up. Another malfunction may be improper insulation causing a short in the blower motor circuit. If the motor locks up or a short occurs in the high speed position, there is sufficient amperage in the circuit generally to blow the main fuse to interrupt the circuit. However, if the blower speed control switch is in the medium or lower positions in the case of three speed motors the circuit current may be insufficient to quickly blow the main fuse. If a malfunction occurs in the blower motor system at the lower speeds, and the circuit is not quickly interrupted, a fire hazard may result.
It has been known for many years that a fuse may be electrically heated to increase its sensitivity so that it will blow under over-voltage conditions. Known U.S. patents related to circuit protecting devices are as follows: U.S. Pat. Nos. 1,214,728; 1,279,020; 1,966,466; 2,763,752; 3,735,312; and 3,839,692.
So far as known, the problem has existed for some time in the motor vehicle field relating to the protection of air conditioning and blower motor circuits. Despite the awareness in the industry of the problem, so far as known, no one has come up with a satisfactory marketable solution to the problem. Though it has been known for over fifty years that a fuse may be heated to increase its sensitivity, no one has applied this knowledge to solve the problem of protecting a blower motor circuit. It is the object of this invention to provide a circuit interruptor which will quickly interrupt the circuit of a malfunctioning blower motor system when the blower motor is at lower speeds which may lack sufficient current amperage in the circuit to quickly blow the main fuse. It is the object of this invention to provide a device which is inexpensive and simple to manufacture and which may be readily incorporated in existing air conditioning and heating systems of motor vehicles.